Field of the Invention
The present invention relates to an imaging device, an imaging system, and an image processing method.
Description of the Related Art
In imaging devices such as a CMOS image sensor, a CCD image sensor, or the like, color filters that transmit light of particular wavelengths are formed on a plurality of photoelectric conversion elements arranged in a two-dimensional manner. Various types of combined color filters are possible, and a combination of red (R), green (G), and blue (B), which are primary colors of the additive mixture of colors, and a combination of cyan (Cy), magenta (Mg), and yellow (Ye), which are primary colors of the subtractive mixture of colors, for example are known. Based on signals from pixels having these respective color filters (hereafter, referred to as color pixel), color image data is produced. For improvement of sensitivity of a solid state imaging device or improvement of signal-to-noise ratio (S/N ratio) in image data, there is known an arrangement with an increased ratio of pixels whose color is more likely to provide brightness information. For example, a solid state imaging device in which the ratios of G and Ye color pixels are increased or white (W or clear) pixels (hereafter, referred to as W pixel) which transmit a light of a wide range of visible light are further provided has been proposed. Further, with respect to the arrangement of filters of respective colors, various arrangements such as so-called Bayer arrangement that are suitable for generating color image data have been proposed.
Japanese Patent Application Laid-open No. 2011-91483 discloses a solid state imaging device that has a so-called RGBW arrangement made of R, G, and B color pixels and white pixels and an image processing device that interpolates and generates RGB color image data based on output signals of respective pixels. In Japanese Patent Application Laid-open No. 2011-91483, the device detects an edge direction from the gradient of pixel values of a plurality of W pixels located around a color pixel to be interpolated and performs an interpolation process on a pixel value corresponding to a W pixel in the color pixels based on the edge direction.
In the technique disclosed in Japanese Patent Application Laid-open No. 2011-91483, however, a larger noise signal superimposed on an image may cause a false detection of the edge direction and therefore a pixel value cannot be accurately interpolated. As a result, a false pattern is generated causing a reduction in an image quality.